Phytic acid sensitizer for silver halide emulsions



PHY TIC ACID SENSITIZER FOR SILVER HALlDE EMULSIONS Gustave WilliamMoessen, New Brunswick, N. J assignor to E. I. du Pont de Nemours andCompany, Wilmiug= ton, Del., a corporation of Delaware No Drawing.Application January 5, 1954, Serial No. 402,405

'10 Claims. (Cl. 95-7) This invention is concerned with photographicsilver halide emulsions and emulsion layers and their preparation. Moreparticularly, it relates to photographic silver halide emulsions whichcontain phytic acid or an alkali metal or ammonium salt thereof and apolyoxyalkylene glycol or an ether or ester thereof. Still moreparticularly it relates to water-permeable colloid silver halideemulsions and emulsion layers containing said mixtures of compounds.

An object of this invention is to provide photographic silver halideemulsions of improved properties. Another object is to providephotographic silver halide emulsions which exhibit increased photolyticand development responses. Yet another object is to provide suchemulsions which have good speeds and stability. A related object is toprovide such emulsions which have low fog values upon extended aging. Afurther object is to provide such emulsions which can be made in asimple manner.

Still other objects will be apparent from the following description ofthe invention.

It has been found that the above objects may be attained andphotographic silver halide emulsions and emulsion layers possessing goodsensitometric stability, speed, gamma, and low fog values can be made byincorporating in an aqueous dispersion or emulsion of light sensitivesilver halides in a water-permeable colloid a small amount of (a) phyticacid or. an alkali metal or ammonium salt thereof, and (b) awater-soluble polyoxyalkylene glycol, preferably a polyoxyethyleneglycol, or an ether or ester thereof having a molecular weight of atleast 400 containing at least one linear radical of the formula(-CH2)mO)n wherein m is 2 or 3 and n is a positive number from 7 to 200inclusive. Mixtures of two or more of the compounds of group (a) can beused with one or a mixture of two or more of compounds of group (b).

The phytic acid or phytate salt may be used in an amount from 0.0004 to0.006 mol and preferably from 0.001 to 0.003 mol per mol of silver inthe silver halide emulsion. The polyoxyalkylene compound may be used inan amount of 0.03 to 1.5 grams per mol of silver in the silver halideemulsion depending on the molecular weight and type of polyoxyalkylenecompound used. In the preferred aspect of the invention from 0.04 to 010gram per mole of silver of a polyethylene glycol having an averagemolecular weight of 3600 is incorporated in the silver halide emulsionor dispersion.

The phytic compound can be added to the colloidsilver halide emulsion ordispersion at any stage in its preparation prior to the completion ofthe digestion period. Thus the phytic acid compound may be added to theacqueous media during the silver halide precipitation step, during theripening period, or prior to or during the initial stages of thedigestion step but are preferably added just prior to, or during theearly stages of, the digestion period. The polyoxyalkylene compoundpreferably is added after the digestion period. The aqueous emulsions ordispersions are. then. prepared for coating 2,757,089 Patented July 31,1956 in any usual manner and coated onto a suitable plate, film or papersheet to form a light-sensitive layer.

Phytic acid (meso-inositol hexaphosphate) and its alkali metal salts, e.g., lithium, sodium and potassium salts and also the ammonium salts areknown compounds and are commercially available. Phytic acid can be madefrom inositol, phosphoric acid and phosphorous pentoxide but is usuallyobtained from natural sources, i. e., plant and animal. It has beenrepresented by the formula:

HCOP OzHg The salts can be made by neutralization of the free acidthiosulfate, and sodium hyposulfite, sensitizing metals and metalcompounds, e. g., gold, palladium, mercury, iron, and thallium and theirchlorides including mixtures of two, three or more of these.

The polyoxyalkylene glycols and their ethers and esters which are usefulin the present invention may be represented by the general formula:

wherein R is a member taken from the group consisting of hydrogen andaliphatic acyl radicals of 1 to 18 or more carbon atoms, R is a membertaken from the class consisting of hydrogen and aliphatic acyl radicalsof 1 to 18 or more carbon atoms and which may be the same or differentfrom R and n is 7 to 200 or more. Their preparation is described in TheChemistry of Synthetic Resins, pages 990-994, published by ReinholdPublishing Corp. (1935).

The carboxylic acid esters can be made by acylating or esterifying theglycols with one or two mols of a carboxylic acid or a carboxylic acidchloride or anhydride so that one or both of the hydroxyl groups of thepolyglycols are converted into ester groups. Among the useful specificagents useful for such reactions are: acetic acid, caproic acid,pelargonic acid, myristic acid, lauric acid, oleic acid, ricinoleicstearic acid, propionyl chloride, valeryl chloride, heptoyl chloride,palmityl chloride, butyric anhydride, etc. Such esters can be madeaccording to the process of Example 2 of Schoeller et al. U. S.1,970,578.

Useful polyoxyalkylene ethers include those of the formula:

wherein R" is an alkyl radical of l to 18 carbon atoms including methyl,ethyl, propyl, dodecyl, etc.

Other suitable ethers and esters include the polyoxyalkylene ethers ofhexitol ring dehydration products. They are essential non-ionic incharacter and can be made by reacting hexitan or hexide with an alkyleneoxide, e. g., ethylene oxide or propylene oxide to introduce two to 20or more oxyalkylene groups in one or more chains and, if desired, with amonofunctional etherification agent or esterification agent to introducea lipophilic group, e. g., an aliphatic hydrocarbon chain of 8 to 18 ormore carbon atoms or the hexitans or hexides may be firstesterified oretherified with such agents and the resulting long chain ethersor esterslater reacted with an alkylene oxide. Suitable long chain etherificationor esterification reactants include normal alkyl halides of 8 to 20carbon atoms, e. g., nroctylchloride, n-dodecyl bromide,n-tetradecylchloride, n-octadecyl bromide, and n-hexadecylbromide, or afatty acid halide of 8 to 20 carbon atoms, e. g., octadecoylchloride,dodecoylchloride, tetradecoyl bromide, n-oleyl chloride, etc.

' A class of especially useful products have a structure which isexemplified by the following hexitans and hexide derivative formulae:

wherein in the formulae one of the Rs is an alkyl radical of 8 to 20carbon atoms or an acyl radical of the formula R-CO- wherein R is of thesame order and the other Rs are hydrogen and n is 2 to 20 or more. Whenonly one (CH2CH2O)n radical is present then it should be 6 or more.

The polyoxyalkylene compounds described above have been used inphotographic emulsions and while commercially useful show markedimprovements when admixed with phytic acid and/or its alkali metal orammonium salts inaccordance with this invention. The latter compoundshave a synergistic eifect and the combinations confergreater sensitizingaction than the compounds used alone. The combinations of the twoclasses of compounds (a) and (b) of this invention increase thesensitivity of silver halide emulsions throughout the whole range of thespectrum. The emulsions have lower fog levels upon aging than thepolyoxyalkylene glycols and their ethers'and estersand mixtures withlowerglycols, e. g., ethylene and propylene glycol.

The invention will be further illustrated, but is not intended to belimited by the following examples wherein the emulsion preparation andsubsequent operations are carried out in the substantial absence ofactinic light.

Example I A washed undigested highly sensitive gelatin siliver halideemulsion containing approximately 1.5% silver iodide and 98.5% silverbromide was divided into 3 parts. To the first part was added 0.00202mol of phytic acid per mol of silver, to the second part was added anequivalent number of mols of sodium hexametaphosphate (0.00202 mol ofhexametaphosphate per mol of silver) and the third portion was reservedas a control. The pl-Is of the three portions were adjusted to 6.3 with3-normal NaOH and the same digestion treatment was given to eachportion. After digestion, each of the three portions was subdivided intotwo equal parts and to the first of each subdivision is added 0.050 gramof polyethylene glycol having an average molecular weight of 3600. Thesame remaining post digestion additions were then made to all sixportions and'they were coated onto a suitable film base and dried. Thecoated filmswere then exposed, developed and fixed with the followingsensitometric results:

as that in Example I, there was added 0.00202 mol of phytic acid per molof silver and a second portion was used as the control. The pH of eachportion was adjusted to 6.3 with 3-normal NaOH and the same digestiontreatment was given to each portion. After digestion, each portion wassubdivided into two equal portions and to one of the sub-portions wasadded 0.050 gram per gram mol of silver of a polyethylene glycol havingan average molecular Weight of 3600. The same normal postdigestionadditions were made to all four portions. The emulsions were coated ontoa suitable film base dried and the coated films were exposed, fixed,washed and dried and tested and the following sensitometric data wereobtained:

as that in Example I there was added 0.00126 mol of phytic acid per molof silver and a like portion was reserved as a control. The pH'of eachportion was adjusted to 6.3 with 3-normal NaOH and the same digestiontreatmentjwas given to both portions. After digestion each portion wassubdivided into two equal parts. To the first portion of eachsubdivision there was added 0.050 gram permol of silver of apolyethylene glycol having an average molecular weight of 3600. Otherpostdigestion additions were the same to all four portions. Theemulsions were coated onto a suitable film base and dried. The coatedfilms were exposed, fixed, washed and dried and tested. The followingsensitometric data were obtained:

To one portion of a washed gelatino silver iodobromide emulsion havingthe sameconstitution as that in Example I there was added 0.00101 moleof phytic acid per mol of silver. A like portion was retained ascontrol. The pH of each part was adjusted to the same value as inExample I and, both parts were given the same digestion treatment. Afterdigestion, to each portion there was added a polyethyleneoxide-ricinoleic acid ester having a molecular weight of approximately1000 in an amount of 0.50 gram of .the ester per mol of silver. Otherpostdigestion additions were the same for both portions. The emulsionswere-coated onto asuitable film base and dried. The coated films wereexposed, fixed, washed and dried and tested. The following sensitometricdata were obtained:

The invention is not limited to the preparation of colloid silveriodobromide emulsions as illustrated in the foregoing examples, but canbe used in emulsions containing other simple or mixed silver halides, e.g., silver chloride, silver bromide, silver chlorobromide, silverchloroiodobromide, etc., emulsions.

Similarly, the invention is not limited to the use of gelatin as thepeptizing or dispersing or binding agent for the silver halide grains.Thus various other water-permeable or hydrophilic colloids, includingthose having reversible characteristics, can be substituted for all, ora portion of the gelatin. Suitable additional colloids include agaragar, polyglycuronic acid, zein, colloidon, water-soluble cellulosederivatives, e. g., hydrolyzed cellulose acetate, cellulose lactate,cellulose glycollate, cellulose acid phthalate and its alkali metalsalts; polyvinyl alcohol, partially hydrolyzed polyvinyl esters andpolyvinyl acetals including those containing color former nuclei,polyamides (water-permeable), poly( 1,3-dioxolanes) polymethacrylicacids and copolymers thereof with other vinyl compounds, e. g., styrene,isobutylene, acrylonitrile, etc., and other synthetic or natural resinsand superpolymers having hydrophilic or water-perrneable characteristicsand which are capable of forming smooth, hard films.

The emulsions can, of course, be coated onto various types of film basesincluding cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cellulose propionate, and cellulose nitrate andfilms made from superpolymers, e. g., nylon, polyethylene terephthalate,polystyrene, polyvinyl chloride and copolymers thereof, e. g.,poly(vinyl chloride co vinyl acetate), etc., paper and any of the usualsheet supports used for making photographic films and papers.

The photographic films bearing above emulsions which contain phytic acidor an alkali or ammonium salt of phytic acid and the polyoxyalkylenecompound can be used for various purposes including camera or portraitfilm, motion picture film, lithographic film, and X-ray film. Theemulsions are especially useful in medical X-ray films and providestable, high-speed medical X-ray films which have high block speeds andgammas and low fog values, even when stored for relatively long periodsof time.

This invention has the advantage that it provides a simple and effectivemeans for providing silver halide emulsions of high speeds and lowdevelopment fog values. Another advantage is that it provides silverhalide emulsions which have good stability upon aging. A furtheradvantage is that the emulsion adjuvants are economical and theirincorporation in emulsions does not require any tedious or involvedprocedure.

I claim:

1. A photographic emulsion comprising light-sensitive silver halidegrains dispersed in a water-permeable colloid containing a small amountof a compound taken from the group consisting of phytic acid and itsalkali metal and ammonium salts and a small amount of a compound takenfrom the group consisting of water-soluble polyoxyalkylene glycol andits ethers and esters having a molecular weight of at least 400containing at least one linear radical of the formula (CH2)m-O)n whereinm is a positive integer from 2 to 3 and n is a positive number from 7 to200.

" 2. A photographic emulsion comprising light-sensitive "silver halidegrains dispersed in a water-permeable colloid containing 0.0004 to 0.006mol of a compound taken from the group consisting of phytic acid and itsalkali metal and ammonium salts and 0.03 to 1.5 grams of a compoundtaken from the group consisting of water-soluble polyoxyalkylene glycoland its ethers and esters having a molecular weight of at least 400containing at least one linear radical of the formula (CH2)m-O)n whereinm is a positive integer from 2 to 3 and n is a positive number from 7 to200, per mol of silver in said silver halide grains.

3. A photographic emulsion comprising light-sensitive silver halidegrains dispersed in a water-permeable colloid containing 0.001 to 0.003gram mol of a compound taken from the group consisting of phytic acidand its alkali metal and ammonium salts and 0.03 to 1.5 grams of acompound taken from the group consisting of water-solublepolyoxyalkylene glycol and its ethers and esters having a molecularweight of at least 400 containing at least one linear radical of theformula (CH2)7n--O)n wherein m is a positive integer from 2 to 3 and nis a positive number from 7 to 200, per mol of silver in said silverhalide grains.

4. An emulsion as set forth in claim 3 wherein said colloid is gelatin.

5. A photographic emulsion comprising light-sensitive silver halidegrains dispersed in a water-permeable colloid containing from 0.0004 to0.006 mol of phytic acid and 0.03 to 1.5 grams of a polyoxyethyleneglycol having a molecular weight of at least 400 per mol of silver insaid emulsion.

6. An emulsion as set forth in claim 5 wherein said colloid is gelatin.

7. A photographic emulsion comprising light-sensitive silver halidegrains dispersed in a water-permeable colloid containing from 0.0004 to0.006 mol of sodium phytate and 0.03 to 1.5 grams of a polyoxyethyleneglycol having a molecular weight of at least 400 per mol of silver insaid emulsion.

8. A photographic element comprising a sheet support bearing a layer ofemulsion as set forth in claim 1.

9. The process of making a photographic silver halide emulsion involvingprecipitation, washing and digestion operations, the step whichcomprises admixing with said emulsion, at some stage prior to thecompletion of the final digestion operation a small amount of a compoundtaken from the group consisting of phytic acid and its alkali metal andammonium salts and after the digestion period a small amount of acompound taken from the group consisting of water-solublepolyoxyalkylene glycol and its ethers and esters having a molecularweight of at least 400 containing at least one linear radical of theformula (CH2)mO)n wherein m is a positive integer from 2 to 3 and n is apositive number from 7 to 200.

10. The process of making a photographic silver halide emulsioninvolving precipitation, washing and digestion operations, the stepwhich comprises admixing with said emulsion, at some stage prior to thecompletion of the final digestion operation 0.0004 to 0.006 mol of acompound taken from the group consisting of phytic acid and its alkalimetal and ammonium salts and after the digestion period 0.03 to 1.5grams of a compound taken from the group consisting of water-solublepolyoxyalkylene glycol and its ethers and esters having a molecularweight of at least 400 containing at least one linear radical of theformula (CH2)m-O)n wherein m is a positive integer from 2 to 3 and n isa positive number from 7 to 200, per mol of silver in said silver halidegrains.

References Cited in the file of this patent UNITED STATES PATENTS1,574,943 Sheppard Mar. 2, 1926 1,591,499 Sheppard July 6, 19262,400,532 Blake May 21, 1946 2,423,549 Blake July 8, 1947 2,441,389Blake May 11, 1948 OTHER REFERENCES Thorpe: Dictionary of Applied Chem,publ. Longmans Green & Company, New York, 1924, vol. V, page 281.

1. A PHOTOGRAPHIC EMULSION COMPRISING LIGHT-SENSITIVE SILVER HALIDEGRAINS DISPERSED IN A WATER-PERMEABLE COLLOID CONTAINING A SMALL AMOUNTOF A COMPOUND TAKEN FROM THE GROUP CONSISTING OF PHYTIC ACID AND ITSALKALI METAL AND AMMONIUM SALTS AND A SMALL AMOUNT OF COMPOUND TAKENFROM THE GROUP CONSISTING OF WATER-SOLUBLE POLYOXYALKYLENE GLYCOL ANDITS ETHERS AND ESTERS HAVING A MOLECULAR WEIGHT OF AT LEAST 400CONTAINING AT LEAST ONE LINEAR RADICAL OF THE FORMULA (-CH2)M-O)NWHEREIN M IS A POSITIVE INTEGER FROM 2 TO 3 N IS A POSITIVE NUMBER FROMTIVE INTEGER FROM 2 TO 3 AND N IS A POSITIVE NUMBER FROM 7 TO 200.